Does abnormal insulin action or insulin secretion explain the increase in prevalence of impaired glucose metabolism with age in populations of different ethnicities?

Background: Age is associated with both impaired glucose and insulin metabolism. To what extent the age-related changes in insulin resistance (IR) and β-cell function contribute to the increase in prevalence of impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) is less known, and this is investigated in this study. Methods: This study included 6610 men and 7664 women of different ethnic groups aged 30-69 years. IR and β-cell function were examined by the homeostasis model assessment of insulin resistance (HOMA-IR) and homeostasis model assessment of β-cell function (HOMA-B). Odds ratios (ORs) and 95% confidence intervals (95% CIs) were estimated using logistic regression analysis adjusting for body mass index and study. Results: In Chinese men, the ORs (95% CIs) for IFG were 2.69 (1.70, 4.26), 2.51 (1.49, 4.21) and 2.89 (1.68, 4.97), respectively, in age groups of 40-49, 50-59 and 60-69 years compared with 30-39 years (p < 0.001 for trend); the corresponding figures for IGT were 1.73 (1.25, 2.38), 2.54 (1.78, 3.63) and 3.57 (2.46, 5.19) (p < 0.001 for trend). Similar trends for IGT were observed also in Chinese women and other ethnic groups, but not for IFG in Mauritius Indian and Creole men. Adjustment for HOMA-IR and HOMA-B reduced the ORs in all age groups of all ethnicities for both IFG and IGT, but the risk gradient between age groups remained particularly for the IGT. Conclusions: The age-related increase in glucose intolerance may not be fully explained by the defect in HOMA-IR and HOMA-B. As HOMA-IR and HOMA-B are only surrogate measures of insulin sensitivity and insulin secretion, the results need to be further investigated.